Materials making use of magnetostriction such as those represented by 12Cr-3Al-Fe, Mn-Cu base alloys and cast iron have been known as vibration-damping materials for a long time. In recent years, sandwich steel sheets having a plastic material between steel plates have been put to practical use.
Of these conventional art vibration-damping materials, the materials making use of magnetostriction such as those represented by 12Cr-3Al-Fe or the Mn-Cu base alloys have had the disadvantages that their vibration-damping properties do not only decrease markedly by plastic working, but drop with increases in temperature. Hence, the critical temperatures for use are 380.degree. C. for the former and 80.degree. C. for the latter. Another problem of such materials has been that their product cost is high. Although cast iron is also a material of which vibration-damping properties have been noted from of old, its vibration-damping properties are not so excellent. The cast iron only produces its vibration-damping properties on its own mass. Albeit inexpensive, the cast iron has the disadvantage that it cannnot be used as the structural material having a limited sectional area, since it is not only poor in plastic workability and weldability but has low strength and is unstable. Referring further to the sandwich steel sheet having a plastic material interposed between steel plates, which is now the most noticeable vibration-damping material in view of its excellent vibration-damping properties and plastic workability, some problems have arisen in that it can only stand up to use at a temperature of as low as 100.degree. C., and is thus not only poor in heat resistance, but is also lacking weldability due to the absence of conductivity, since the platic material is used as the material to attain vibration-damping properties.
Still further, an extremely special vibration-damping material has been proposed, which is obtained by the procedures comprising the steps of subjecting the surface layer of a metal sheet to an intergranular oxidation, a sensitizing or a mechanical treatment to give flaws to the surface thereof, and subjecting the metal sheet having its surface layer thus processed to processing such as cold rolling to introduce intergranular fracture or converting the surface flaws to scab marks, thereby attaining vibration-damping properties. However, the vibration-damping material obtained by such procedures offers some problems in that its plastic workability is poor due to the presence of surface fractures, and its fatigue strength drops markedly so that is reliability as a structural material becomes poor.